Method of Controlling a Motorized Window Treatment

ABSTRACT

A method comprises measuring a light intensity at a window; determining if the light intensity exceeds a cloudy-day threshold; operating in a sunlight penetration limiting mode to control the motorized window treatment to control the sunlight penetration distance in the space; enabling the sunlight penetration limiting mode if the light intensity is greater than the cloudy-day threshold; and disabling the sunlight penetration limiting mode if the total lighting intensity is less than the cloudy-day threshold. The cloudy-day threshold is maintained at a constant threshold if a calculated solar elevation angle is greater than a predetermined solar elevation angle, and the cloudy-day threshold varies with time if the calculated solar elevation angle is less than the predetermined solar elevation angle. The cloudy-day threshold is a function of the calculated solar elevation angle if the calculated solar elevation angle is less than the predetermined solar elevation angle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.15/799,461, filed on Oct. 31, 2017 (now U.S. Pat. No. 10,663,935, Issuedon May 26, 2020), which is a continuation of U.S. patent applicationSer. No. 13/838,876, filed on Mar. 15, 2013 (now U.S. Pat. No.9,933,761, Issued on Apr. 3, 2018), which claims the benefit of U.S.Provisional Patent Application No. 61/731,844, filed on Nov. 30, 2012,each of which is incorporated by reference herein in its entirety.

FIELD

The present invention relates to a load control system for controlling aplurality of motorized window treatments in a space, and moreparticularly, to a procedure for automatically controlling one or moremotorized window treatments to prevent direct sun glare on work spacesin the space.

BACKGROUND

Motorized window treatments, such as, for example, motorized rollershades and draperies, provide for control of the amount of sunlightentering a space. Some prior art motorized window treatments have beenautomatically controlled in response to various inputs, such as daylightsensors and timeclocks, to control the amount of daylight entering aspace to adjust the total lighting level in the space to a desiredlevel. For example, the load control system may attempt to maximize theamount of daylight entering the space in order to minimize the intensityof the electrical lighting in the space. In addition, some prior artload control systems additionally controlled the positions of themotorized window treatments to prevent sun glare in the space toincrease occupant comfort, for example, as described in greater detailin commonly-assigned U.S. Pat. No. 7,950,827, issued May 31, 2011,entitled ELECTRICALLY CONTROLLABLE WINDOW TREATMENT SYSTEM TO CONTROLSUN GLARE IN A SPACE, the entire disclosure of which is herebyincorporated by reference.

One prior art load control system controlled the position of motorizedroller shades to limit the sunlight penetration depth in the space to amaximum penetration depth while minimizing movements of the rollershades to minimize occupant distractions, as described incommonly-assigned U.S. Pat. No. 8,288,981, issued Oct. 16, 2012,entitled METHOD OF AUTOMATICALLY CONTROLLING A MOTORIZED WINDOWTREATMENT WHILE MINIMIZING OCCUPANT DISTRACTIONS, the entire disclosureof which is hereby incorporated by reference. Specifically, the loadcontrol system controls the position of the motorized roller shades inresponse to a calculated position of the sun to thus limit the sunlightpenetration depth in the space on sunny days. During a cloudy day, theload control system is operable to stop controlling the motorized windowtreatments to limit the sunlight penetration depth to the maximumpenetration depth and to simply adjust the positions of the motorizedwindow treatments to predetermined positions. For example, the loadcontrol system may comprise a photosensor (i.e., a daylight sensor or aradiometer) mounted to a window or to the outside of the building fordetecting a cloudy condition. The load control system may detect thecloudy condition, for example, if a total light level measured by thephotosensor is below a constant threshold TH_(CONST).

FIGS. 1 and 2 show example plots of the total light level L_(SENSOR)measured by the photosensor on a sunny day and a cloudy day,respectively. On both sunny and cloudy days, the total light levelL_(SENSOR) measured by the photosensor increases from zero at sunrise(i.e., at time t_(SUNRISE)) and then begins to decrease toward zero atsunset (i.e., at time t_(SUNSET)). On the cloudy day shown in FIG. 2,the total light level L_(SENSOR) measured by the photosensor does notexceed the constant threshold TH_(CONST), such that the load controlsystem controls the motorized window treatments to predeterminedpositions (i.e., the load control system will not control the motorizedwindow treatments to limit the sunlight penetration depth to the maximumpenetration depth at any point in the day). On the sunny day shown inFIG. 1, the load control system begins to control the motorized windowtreatments to limit the sunlight penetration depth to the maximumpenetration depth when the total light level L_(SENSOR) measured by thephotosensor exceeds the constant threshold TH_(CONST) at timet_(ENABLE,)and then stops controlling the motorized window treatments tolimit the sunlight penetration depth to the maximum penetration depthwhen the total light level L_(SENSOR) measured by the photosensor dropsbelow the constant threshold TH_(CONST) at time t_(DISABLE).

However, on the sunny day near sunrise and sunset as shown in FIG. 1,the load control system may mistakenly conclude that the present day iscloudy when the total light level L_(SENSOR) measured by the photosensoris less than the constant threshold TH_(CONST) (i.e., betweent_(SUNRISE) and t_(ENABLE) and between t_(DISABLE) and t_(SUNSET)). Atthese times, the sun may be very low in the sky and may shine directlyinto the windows of the building, thus creating glare conditions. Thus,there is a need for a load control system that is able to moreaccurately distinguish between sunny and cloudy days in order to preventglare around sunrise and sunset on sunny days.

SUMMARY

In some embodiments, a method of controlling a motorized windowtreatment is provided for adjusting the amount of sunlight entering aspace of a building through a window to control a sunlight penetrationdistance in the space. The method comprises: (1) measuring a total lightintensity at the window; (2) determining if the total light intensityexceeds a cloudy-day threshold; (3) operating in a sunlight penetrationlimiting mode to control the motorized window treatment to thus controlthe sunlight penetration distance in the space; (4) enabling thesunlight penetration limiting mode if the total light intensity isgreater than the cloudy-day threshold; and (5) disabling the sunlightpenetration limiting mode if the total lighting intensity is less thanthe cloudy-day threshold. According to one embodiment of the presentinvention, the cloudy-day threshold is maintained at a constantthreshold if a calculated solar elevation angle is greater than apredetermined solar elevation angle, and the cloudy-day threshold varieswith time if the calculated solar elevation angle is less than thepredetermined solar elevation angle. According to another embodiment ofthe present invention, the cloudy-day threshold is a function of thecalculated solar elevation angle if the calculated solar elevation angleis less than the predetermined solar elevation angle.

In some embodiments, a method of controlling a motorized windowtreatment positioned adjacent to a window on a wall of a buildingcomprises: sampling a total light intensity outside of the building;computing a rate of change of the total light intensity; automaticallycontrolling movement of the window treatment in a sunny operation modeif the computed absolute value of the rate of change is at least a firstthreshold value; and automatically controlling movement of the windowtreatment in a cloudy operation mode if the computed absolute value ofthe rate of change is less than the first threshold value and the totallight intensity is less than a second threshold value.

In some embodiments, a method of controlling a motorized windowtreatment positioned adjacent to a window on a wall of a buildingcomprises: (a) sampling a total light intensity outside of the building;(b) computing a rate of change of the total light intensity; (c)automatically controlling movement of the window treatment based on thetotal light intensity if the total light intensity is at least a firstthreshold value; and (d) automatically controlling movement of thewindow treatment based at least partially on an absolute value of therate of change of the total light intensity if the total light intensityis less than the first threshold value.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example plot of a total light level measured aphotosensor located on a building on a sunny day.

FIG. 2 shows an example plot of a total light level measured aphotosensor located on a building on a cloudy day.

FIG. 3 is a simplified block diagram of a load control system having atleast one motorized roller shade and a cloudy-day sensor according to anembodiment of the present invention.

FIG. 4 is a simplified side view of an example of a space of a buildinghaving a window covered by the motorized roller shade of the loadcontrol system of FIG. 3.

FIG. 5A is a side view of the window of FIG. 4 illustrating a sunlightpenetration depth.

FIG. 5B is a top view of the window of FIG. 4 when the sun is directlyincident upon the window.

FIG. 5C is a top view of the window of FIG. 4 when the sun is notdirectly incident upon the window.

FIG. 6 shows an example plot of the total light level measured by thecloudy-day sensor of the load control system of FIG. 3 on a sunny dayand a cloudy-day threshold according to the embodiment of the presentinvention.

FIG. 7 is a simplified flowchart of a cloudy-day procedure according tothe embodiment of the present invention.

FIG. 8 is a schematic diagram of another embodiment of an automatedwindow treatment system.

FIG. 8A is a block diagram of a sensor used in some embodiments of themotorized window treatment shown in FIG. 8.

FIG. 9 is a flow chart of a method of operating the system of FIG. 8.

FIGS. 10A-10C show alternative details of block 912 of FIG. 9.

FIG. 11 is a detailed flow chart of an embodiment of the method of FIG.9.

FIGS. 12A-12B show alternative details of the cloudy day operation mode.

FIG. 13A is a flow chart of a variation of the method of FIG. 9.

FIGS. 13B and 13C are alternative diagrams of block 1310 of FIG. 13A.

FIG. 14 is a state diagram showing the permissible state changes betweenthe sunny day mode and cloudy day mode.

FIG. 15 shows an example of the rate-of-change over time, where twothresholds are used to provide hysteresis for change of operating mode.

DETAILED DESCRIPTION

This description of the exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description, relativeterms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,”“below,” “up,” “down,” “top” and “bottom” as well as derivative thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should beconstrued to refer to the orientation as then described or as shown inthe drawing under discussion. These relative terms are for convenienceof description and do not require that the apparatus be constructed oroperated in a particular orientation. Terms concerning attachments,coupling and the like, such as “connected” and “interconnected,” referto a relationship wherein structures are secured or attached to oneanother either directly or indirectly through intervening structures, aswell as both movable or rigid attachments or relationships, unlessexpressly described otherwise.

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustrating theinvention, there is shown in the drawings an embodiment that ispresently preferred, in which like numerals represent similar partsthroughout the several views of the drawings, it being understood,however, that the invention is not limited to the specific methods andinstrumentalities disclosed.

FIG. 3 is a simplified block diagram of a load control system 100according to an embodiment of the present invention. The load controlsystem 100 is operable to control the level of illumination in a spaceby controlling the intensity level of the electrical lights in the spaceand the daylight entering the space. As shown in FIG. 3, the loadcontrol system 100 is operable to control the amount of power deliveredto (and thus the intensity of) a plurality of lighting loads, e.g., aplurality of fluorescent lamps 102. The load control system 100 isfurther operable to control the position of a plurality of motorizedwindow treatments, e.g., motorized roller shades 104, to control theamount of sunlight entering the space. The motorized window treatmentscould alternatively comprise motorized draperies, blinds, roman shades,or skylight shades. The load control system comprises a plurality oflighting hubs 140, which act as central controllers for managing theoperation of the lighting loads (i.e., the plurality of fluorescentlamps 102) and the motorized window treatments (i.e., the motorizedroller shades 104).

Each of the fluorescent lamps 102 is coupled to one of a plurality ofdigital electronic dimming ballasts 110 for control of the intensitiesof the lamps. The ballasts 110 are operable to communicate with eachother via digital ballast communication links 112 (i.e., the ballastsare operable to transmit digital messages to the other ballasts via thedigital ballast communication links). Each digital ballast communicationlink 112 is also coupled to a digital ballast controller (DBC) 114,which provides the necessary direct-current (DC) voltage to power thecommunication link 112 and assists in the programming of the loadcontrol system 100. For example, the digital ballast communication link112 may comprise a digital addressable lighting interface (DALI)communication link. The lighting hubs 140 are coupled to the digitalballast controllers 114 via respective lighting hub communication links142, such that the lighting hubs are operable to transmit digitalmessages to the ballasts 110.

Each of the motorized roller shades 104 comprises an electronic driveunit (EDU) 130, which may be located, for example, inside a roller tubeof the associated roller shade. Each electronic drive units 130 iscoupled to one of the lighting hub communication links 142 for receivingdigital messages from the respective lighting hub 140. An example of amotorized window treatment control system is described in greater detailin commonly-assigned U.S. Pat. No. 6,983,783, issued Jun. 11, 2006,entitled MOTORIZED SHADE CONTROL SYSTEM, the entire disclosure of whichis hereby incorporated by reference. Alternatively, the lighting hubs140 may be operable to transmit wireless signals, for example,radio-frequency (RF) signals, to the electronic drive units 130 forcontrolling the motorized roller shades. Examples of a radio-frequencymotorized window treatments are described in greater detail incommonly-assigned U.S. Pat. No. 7,723,939, issued May 25, 2010, entitledRADIO-FREQUENCY CONTROLLED MOTORIZED ROLLER SHADE, and U.S. PatentApplication Publication No. 2012/0261078, published Oct. 18, 2012,entitled MOTORIZED WINDOW TREATMENT, the entire disclosures of which arehereby incorporated by reference.

The load control system 100 further comprises wallstations 144, 146coupled to the lighting hub communication links 142 for controlling theload control devices (i.e., the ballasts 110 and the electronic driveunits 130) of the load control system. For example, actuations ofbuttons on the first wallstation 144 may turn one or more of the lamps102 on and off or adjust the intensities of one or more of the lamps. Inaddition, actuations of the buttons of the second wallstation 146 mayopen or close the one or more of the motorized roller shades 104, adjustthe positions of one or more of the motorized roller shades, or controlone or more of the motorized roller shades to preset shade positionsbetween an open-limit position (e.g., a fully-open position P_(FO)) anda closed-limit position (e.g., a fully-closed position P_(FC)).

The lighting hubs 140 are further coupled to a personal computer (PC)150 via a network (e.g., having an Ethernet link 152 and a standardEthernet switch 154), such that the PC is operable to transmit digitalmessages to the ballasts 110 and the electronic drive units 130 via thelighting hubs 140. The PC 150 executes a graphical user interface (GUI)software, which is displayed on a PC screen 156. The GUI software allowsthe user to configure and monitor the operation of the load controlsystem 100. During configuration of the lighting control system 100, theuser is operable to determine how many ballasts 110, digital ballastcontrollers 114, electronic drive units 130, and lighting hubs 140 thatare connected and active using the GUI software. Further, the user mayalso assign one or more of the ballasts 110 to a zone or a group, suchthat the ballasts 110 in the group respond together to, for example, anactuation of a wallstation. The lighting hubs 140 may also be operableto receive digital messages via the network from a smart phone (e.g., aniPhone® smart phone, an Android® smart phone, or a Blackberry® smartphone), a tablet (e.g., an iPad® hand-held computing device), or anyother suitable Internet-Protocol-enabled device.

The load control system 100 may operate in a sunlight penetrationlimiting mode to control the amount of sunlight entering a space 160(FIG. 4) of a building to control a sunlight penetration distanced_(PEN) in the space. Specifically, the lighting hubs 140 are operableto transmit digital messages to the motorized roller shades 104 tocontrol the sunlight penetration distance d_(PEN) in the space 160. Eachlighting hub 140 comprises an astronomical timeclock and is able todetermine the sunrise time t_(SUNRISE) and the sunset time t_(SUNSET)for each day of the year for a specific location. The lighting hubs 140each transmit commands to the electronic drive units 130 toautomatically control the motorized roller shades 104 in response to atimeclock schedule. Alternatively, the PC 150 could comprise theastronomical timeclock and could transmit the digital messages to themotorized roller shades 104 to control the sunlight penetration distanced_(PEN) in the space 160.

The load control system 100 further comprises a cloudy-day sensor 180that may be mounted to the inside surface of a window 166 (FIG. 4) inthe space 160 or to the exterior of the building. The cloudy-day sensor180 may be battery-powered and may be operable to transmit wirelesssignals, e.g., radio-frequency (RF) signals 182, to a sensor receivermodule 184 as shown in FIG. 3. The sensor receiver module 184 isoperable to transmit digital messages to the respective lighting hub 140via the lighting hub communication link 142 in response to the RFsignals 182 from the cloudy-day sensor 180. Accordingly, in response todigital messages received from the cloudy-day sensor 180 via the sensorreceiver module 184, the lighting hubs 140 are operable to enable anddisable the sunlight penetration limiting mode as will be described ingreater detail below. The load control system 100 may comprise aplurality of cloudy-day sensors located at different windows around thebuilding (as well as a plurality of sensor receiver modules), such thatthe load control system 100 may enable the sunlight penetration limitingmode in some areas of the building and not in others. Alternatively, thecloudy-day sensor 180 may be coupled to the sensor receiver module 184via a wired control link or directly coupled to the lighting hubcommunication link 142.

FIG. 4 is a simplified side view of an example of the space 160illustrating the sunlight penetration distance d_(PEN), which iscontrolled by the motorized roller shades 104. As shown in FIG. 4, thebuilding comprises a façade 164 (e.g., one side of a four-sidedrectangular building) having a window 166 for allowing sunlight to enterthe space. The space 160 also comprises a work surface, e.g., a table168, which has a height h_(WORK). The cloudy-day sensor 180 may bemounted to the inside surface of the window 166 as shown in FIG. 4. Themotorized roller shade 104 is mounted above the window 166 and comprisesa roller tube 172 around which the shade fabric 170 is wrapped. Theshade fabric 170 may have a hembar 174 at the lower edge of the shadefabric. The electronic drive unit 130 rotates the roller tube 172 tomove the shade fabric 170 between the fully-open position P_(FO) (inwhich the window 166 is not covered) and the fully-closed positionP_(FC) (in which the window 166 is fully covered). Further, theelectronic drive unit 130 may control the position of the shade fabric170 to one of a plurality of preset positions between the fully-openposition P_(FO) and the fully-closed position P_(FC).

The sunlight penetration distance d_(PEN) is the distance from thewindow 166 and the façade 164 at which direct sunlight shines into theroom. The sunlight penetration distance d_(PEN) is a function of aheight h_(WIN) of the window 166 and an angle ϕ_(F) of the façade 164with respect to true north, as well as a solar elevation angle θ_(S) anda solar azimuth angle ϕ_(S), which define the position of the sun in thesky. The solar elevation angle θ_(S) and the solar azimuth angle ϕ_(S)are functions of the present date and time, as well as the position(i.e., the longitude and latitude) of the building 162 in which thespace 160 is located. The solar elevation angle θ_(S) is essentially theangle between a line directed towards the sun and a line directedtowards the horizon at the position of the building 162. The solarelevation angle θ_(S) can also be thought of as the angle of incidenceof the sun's rays on a horizontal surface. The solar azimuth angle ϕ_(S)is the angle formed by the line from the observer to true north and theline from the observer to the sun projected on the ground. When thesolar elevation angle θ_(S) is small (i.e., around sunrise and sunset),small changes in the position of the sun result in relatively largechanges in the magnitude of the sunlight penetration distance d_(PEN).

The sunlight penetration distance d_(PEN) of direct sunlight onto thetable 168 of the space 160 (which is measured normal to the surface ofthe window 166) can be determined by considering a triangle formed bythe length

of the deepest penetrating ray of light (which is parallel to the pathof the ray), the difference between the height h_(WiN) of the window 166and the height h_(WORK) of the table 168, and distance between the tableand the wall of the façade 164 (i.e., the sunlight penetration distanced_(PEN)) as shown in the side view of the window 166 in FIG. 5A, i.e.,

tan(θ_(S))≤(h _(WIN) −h _(WORK)/

,   (Equation 51)

where θ_(S) is the solar elevation angle of the sun at a given date andtime for a given location (i.e., longitude and latitude) of thebuilding.

If the sun is directly incident upon the window 166, a solar azimuthangle ϕ_(S) and the façade angle ϕ_(F) (i.e., with respect to truenorth) are equal as shown by the top view of the window 166 in FIG. 5B.Accordingly, the sunlight penetration distance d_(PEN) equals the length

of the deepest penetrating ray of light. However, if the façade angleϕ_(F) is not equal to the solar azimuth angle ϕ_(S), the sunlightpenetration distance d_(PEN) is a function of the cosine of thedifference between the angle ϕ_(F) and the solar azimuth angle ϕ_(S),i.e.,

d_(PEN)=

cos(|ϕ_(F)−ϕ_(S)|),   (Equation 2)

as shown by the top view of the window 166 in FIG. 5C.

As previously mentioned, the solar elevation angle θ_(S) and the solarazimuth angle θ_(S) define the position of the sun in the sky and arefunctions of the position (i.e., the longitude and latitude) of thebuilding in which the space 160 is located and the present date andtime. The following equations are necessary to approximate the solarelevation angle θ_(S) and the solar azimuth angle θ_(S). The equation oftime defines essentially the difference in a time as given by a sundialand a time as given by a clock. This difference is due to the obliquityof the Earth's axis of rotation. The equation of time can beapproximated by

E=9.87·sin(2B)−7.53·cos(B)−1.5·sin(B),   (Equation 3)

where B=[360°·(N_(DAY)−81)]/364, and N_(DAY) is the present day-numberfor the year (e.g., N_(DAY) equals one for January 1, N_(DAY) equals twofor January 2, and so on).

The solar declination δ is the angle of incidence of the rays of the sunon the equatorial plane of the Earth. If the eccentricity of Earth'sorbit around the sun is ignored and the orbit is assumed to be circular,the solar declination is given by:

δ=23.45°·sin[360°/365·(N _(DAY)+284)].   (Equation 4)

The solar hour angle H is the angle between the meridian plane and theplane formed by the Earth's axis and current location of the sun, i.e.,

H(t)={¼·[t+E−(4·λ)+(60·t _(TZ))]}−180°,   (Equation 5)

where t is the present local time of the day, λ is the local longitude,and t_(TZ) is the time zone difference (in unit of hours) between thelocal time t and Greenwich Mean Time (GMT). For example, the time zonedifference t_(TZ) for the Eastern Standard Time (EST) zone is −5. Thetime zone difference t_(TZ) can be determined from the local longitude λand latitude Φ of the building 162. For a given solar hour angle H, thelocal time can be determined by solving Equation 5 for the time t, i.e.,

t=720+4·(H+λ)−(60·t _(TZ))−E.   (Equation 6)

When the solar hour angle H equals zero, the sun is at the highest pointin the sky, which is referred to as “solar noon” time t_(SN), i.e.,

t _(SN)=720+(4·λ)−(60·t _(TZ))−E.   (Equation 7)

A negative solar hour angle H indicates that the sun is east of themeridian plane (i.e., morning), while a positive solar hour angle Hindicates that the sun is west of the meridian plane (i.e., afternoon orevening).

The solar elevation angle θ_(S) as a function of the present local timet can be calculated using the equation:

θ_(S)(t)=sin⁻¹[cos(H(t))·cos(δ)·cos(Φ)+sin(δ)·sin(Φ)],   (Equation 8)

wherein Φ is the local latitude. The solar azimuth angle Φ_(S) as afunction of the present local time t can be calculated using theequation:

Φ_(S)(t)=180°·C(t)·cos⁻¹ [X(t)/cos(θ_(S)(t))],   (Equation 9)

where

X(t)=[cos(H(t))·cos(δ)·sin(Φ)−sin(δ)·cos(Φ)],   (Equation 10)

and C(t) equals negative one if the present local time t is less than orequal to the solar noon time t_(SN) or one if the present local time tis greater than the solar noon time t_(SN). The solar azimuth angleϕ_(S) can also be expressed in terms independent of the solar elevationangle θ_(S), i.e.,

Φ_(S)(t)=tan⁻¹[−sin(H(t))·cos(δ)/Y(t)],   (Equation 11)

where

Y(t)=[sin(δ)·cos(Φ)−cos(δ)·sin(Φ)·cos(H(t))].   (Equation 12)

Thus, the solar elevation angle θ_(S) and the solar azimuth angle ϕ_(S)are functions of the local longitude λ and latitude Φ and the presentlocal time t and date (i.e., the present day-number N_(DAY)). UsingEquations 1 and 2, the sunlight penetration distance can be expressed interms of the height h_(WIN) of the window 166, the height h_(WORK) ofthe table 168, the solar elevation angle θ_(S), and the solar azimuthangle Φ_(S).

As previously mentioned, the lighting hubs 140 may operate in thesunlight penetration limiting mode to control the motorized rollershades 104 to limit the sunlight penetration distance d_(PEN) to be lessthan a desired maximum sunlight penetration distance d_(MAX). Forexample, the sunlight penetration distance d_(PEN) may be limited suchthat the sunlight does not shine directly on the table 168 to preventsun glare on the table. The desired maximum sunlight penetrationdistance d_(MAX) may be entered using the GUI software of the PC 150 andmay be stored in memory in each of the lighting hubs 140. In addition,the user may also use the GUI software of the PC 150 to enter and thepresent date and time, the present timezone, the local longitude λ andlatitude Φ of the building, the façade angle ϕ_(F) for each façade 164of the building, the height h_(WIN) of the windows 166 in spaces 160 ofthe building, and the heights h_(WORK) of the workspaces (i.e., tables168) in the spaces of the building. These operational characteristics(or a subset of these operational characteristics) may also be stored inthe memory of each lighting hub 140. Further, the motorized rollershades 104 are also controlled such that distractions to an occupant ofthe space 160 (i.e., due to movements of the motorized roller shades)are minimized, for example, by only opening and closing each motorizedroller shade once each day resulting in only two movements of the shadeseach day.

The lighting hubs 140 are operable to generate a timeclock scheduledefining the desired operation of the motorized roller shades 104 ofeach of the façades 164 of the building 162 to limit the sunlightpenetration distance d_(PEN) in the space 160. For example, the lightinghubs 140 may generate a new timeclock schedule once each day at midnightto limit the sunlight penetration distance d_(PEN) in the space 160 forthe next day. The lighting hubs 140 are operable to calculate optimalshade positions of the motorized roller shades 104 in response to thedesired maximum sunlight penetration distance d_(MAX) at a plurality oftimes for the next day. The lighting hubs 140 are then operable to use auser-selected minimum time period T_(MIN) between shade movements aswell as the calculated optimal shade positions to generate the timeclockschedule for the next day. Examples of methods of controlling motorizedwindow treatments to minimize sunlight penetration depth using timeclockschedules are described in greater detail in previously-referenced U.S.Pat. No. 8,288,981.

In some cases, when the lighting hub 140 controls the motorized rollershades 104 to the fully-open positions P_(FO) (i.e., when there is nodirect sunlight incident on the façade 164), the amount of daylightentering the space 160 may be unacceptable to a user of the space.Therefore, the lighting hub 140 is operable to set the open-limitpositions of the motorized roller shades of one or more of the spaces160 or façades 164 of the building to a visor position P_(VISOR), whichis typically lower than the fully-open position P_(FO), but may be equalto the fully-open position. Thus, the visor position P_(VISOR) definesthe highest position to which the motorized roller shades 104 will becontrolled during the timeclock schedule. The position of the visorposition P_(VISOR) may be entered using the GUI software of the PC 150.In addition, the visor position P_(VISOR) may be enabled and disabledfor each of the spaces 160 or façades 164 of the building using the GUIsoftware of the PC 150. Since two adjacent windows 166 of the buildingmay have different heights, the visor positions P_(VISOR) of the twowindows may be programmed using the GUI software, such that the hembars174 of the shade fabrics 172 covering the adjacent window are alignedwhen the motorized roller shades 104 are controlled to the visorpositions P_(VISOR).

In response to the RF signals 182 received from the cloudy-day sensor180, the lighting hubs 140 are operable to disable the sunlightpenetration limiting mode (i.e., to stop controlling the motorizedroller shades 104 to limit the sunlight penetration distance d_(PEN)).Specifically, if the total light level L_(SENSOR) measured by thecloudy-day sensor 180 is below a cloudy-day threshold TH_(CLOUDY), eachlighting hub 140 is operable to determine that cloudy conditions existoutside the building and to control one or more of the motorized rollershades 104 to the visor positions P_(VISOR) in order to maximum theamount of natural light entering the space 160 and to improve occupantcomfort by providing a better view out of the window 166. However, ifthe total light level L_(SENSOR) measured by the cloudy-day sensor 180is greater than or equal to the cloudy-day threshold TH_(CLOUDY), eachlighting hub 140 is operable to determine that sunny conditions existoutside the building and to enable the sunlight penetration limitingmode to control the motorized roller shades 104 to limit the sunlightpenetration distance d_(PEN) in the space 160 to thus prevent sun glareon the table 168.

FIG. 6 shows an example plot of the total light level L_(SENSOR)measured by the cloudy-day sensor 180 on a sunny day and the cloudy-daythreshold TH_(CLOUDY) used by the lighting hubs 140 according to theembodiment of the present invention. During most of the day, when thecalculated solar elevation angle θ_(S) is greater than a predeterminedcut-off elevation θ_(CUT-OFF) (e.g., approximately 15°), the cloudy-daythreshold TH_(CLOUDY) is maintained constant, for example, at the priorart constant threshold TH_(CONST) (e.g., approximately 1000foot-candles). To prevent the lighting hubs 140 from mistakenlydetermining that the present day is a cloudy day around sunrise andsunset, the cloudy-day threshold TH_(CLOUDY) is adjusted as a functionof the calculated solar elevation angle θ_(S), e.g.,

$\begin{matrix}{{TH}_{CLOUDY} = {{TH}_{CONST} \cdot \frac{\theta_{s}}{\theta_{{CUT} - {OFF}}}}} & \left( {{Equation}\mspace{14mu} 13} \right)\end{matrix}$

Accordingly, the cloudy-day threshold TH_(CLOUDY) varies with time nearsunrise and sunset, and is maintained at the constant thresholdTH_(CONST) near midday. Since the solar elevation angle θ_(S) isapproximately linear near sunrise and sunset, the cloudy-day thresholdTH_(CLOUDY) is increased somewhat linearly from zero to the cloudy-daythreshold TH_(CLOUDY) from the sunrise time t_(SUNRISE) to timet_(ENABLE), and decrease somewhat linearly from the cloudy-day thresholdTH_(CLOUDY) to zero from time t_(DISABLE) to the sunset time t_(SUNSET)as shown in FIG. 6. Alternatively, the cloudy-day threshold TH_(CLOUDY)could vary with time for a first predetermined time period after sunriseand a second predetermined time period before sunset.

FIG. 7 is a simplified flowchart of a cloudy-day procedure 300 executedby each lighting hub 140 periodically (e.g., once every minute). First,the lighting hub 140 determines the total light level L_(SENSOR) at step310, for example, by recalling from memory the last light levelinformation received from the cloudy-day sensor 180. If, at step 311,the total light level L_(SENSOR) has not changed since the last timethat the cloudy-day procedure 300 was executed, the cloudy-day procedure300 simply exits. However, if the total light level L_(SENSOR) haschanged at step 311, the lighting hub 140 calculates the solar elevationangle θ_(S) at step 312 (e.g., using equations 1-8 as shown above). Ifthe calculated solar elevation angle θ_(S) is greater than the cut-offelevation θ_(CUT-OFF) (i.e., approximately 15°) at step 314, thelighting hub 140 sets the cloudy-day threshold TH_(CLOUDY) to be equalto the prior art constant threshold TH_(CONST) at step 316. If thecalculated solar elevation angle θ_(S) is less than or equal to thecut-off elevation θ_(CUT-OFF) at step 314, the lighting hub 140calculates the cloudy-day threshold TH_(CLOUDY) as a function of theconstant threshold TH_(CONST), the calculated solar elevation angleθ_(S), and the cut-off elevation θ_(CUT-OFF) at step 318 (e.g., as shownin equation 13 above). If, at step 320, the total light level L_(SENSOR)is greater than the cloudy-day threshold TH_(CLOUDY) (as set at step 316or 318), the lighting hub 140 enables the sunlight penetration limitingmode to control the motorized roller shades 104 according to thetimeclock schedule at step 324 (i.e., to limit the sunlight penetrationdistance d_(PEN) in the space 160), and the cloudy-day procedure 300exits. If the total light level L_(SENSOR) is less than or equal to thecloudy-day threshold TH_(CLOUDY) at step 320, the lighting hub 140disables the sunlight penetration limiting mode and controls themotorized roller shades to the visor positions P_(VISOR) at step 324,before the cloudy-day procedure 300 exits.

While the present application has been described with reference todistinguishing between sunny and cloudy days, the concepts of thepresent application can also be applied to other external conditionsthat may affect the amount and direction of sunlight entering the space160, for example, shadow conditions and reflected glare conditionscaused by other buildings and objects. For example, the lighting hubs140 could disable the sunlight penetration limiting mode if thecloudy-day sensor 180 detects that a shadow is on the window 166.

In some embodiments, a method of controlling a motorized windowtreatment for adjusting the amount of sunlight entering a space of abuilding through a window to control a sunlight penetration distance inthe space, the method comprising:

measuring a total light intensity at the window;

calculating a solar elevation angle;

calculating a cloudy-day threshold as a function of the calculated solarelevation angle;

determining if the total light intensity exceeds the cloudy-daythreshold;

operating in a sunlight penetration limiting mode to control themotorized window treatment to thus control the sunlight penetrationdistance in the space;

enabling the sunlight penetration limiting mode if the total lightintensity is greater than the cloudy-day threshold; and

disabling the sunlight penetration limiting mode if the total lightingintensity is less than the cloudy-day threshold.

In some embodiments, the cloudy-day threshold is maintained at aconstant threshold if the calculated solar elevation angle is greaterthan a predetermined solar elevation angle, and the cloudy-day thresholdis a function of the calculated solar elevation angle if the calculatedsolar elevation angle is less than the predetermined solar elevationangle.

Some embodiments further comprise controlling the motorized windowtreatment to a predetermined position when the sunlight penetrationlimiting mode is disabled.

FIG. 8 is a schematic diagram of another embodiment of an automaticwindow treatment system 200, which does not require any externallysupplied power, communications, or data. This system 200 can beconveniently installed by a homeowner without performing any wiring. Thesystem does not require the user to input any time or geographic data,or information about the relative position between the window treatmentand the sun. The system 200 does not require wireless or wiredcommunications with any other home systems.

System 200 includes a window treatment 104, which may be a roller shade.motorized draperies, blinds, roman shades, skylight shades, or the like.The window treatment 104 is equipped with a power source, such as areceptacle (not shown) for holding a battery 206 and receiving DC powerfrom the battery, to power the motor (not shown) for changing theposition of the window treatment 104. In some embodiments, the batteryis a commercially available alkaline, NiCd or Lithium ion battery forexample. The battery can be re-chargeable or disposable. In otherembodiments, the battery is a proprietary internal battery.

The system includes a photosensor 202 which measures the total intensityof the visible light impinging on the photosensor 202. The photosensor202 may be any of a variety of sensors, such as a photometer,radiometer, photodiode, photoresistor or the like. In some embodiments,the sensor 202 is built into the housing of the window treatment 104. Inother embodiments, the photosensor 202 is a separate device which can beinstalled inside or outside of the window, and connected to the controlunit 204 via a wired or wireless connection.

In some embodiments, as shown in FIG. 8A, the photosensor 202 is a“smart device” comprising a sensor 202 a, a microcontroller or embeddedprocessor 202 b, a non-transitory storage medium such as a memory 202 cwith instruction and data storage portions, and a bus 202 d connectingthe sensor, microcontroller and memory, all contained within a singlehousing 202 e. In some embodiments, the sensor, microcontroller orembedded processor, memory, and bus are all mounted on a printed circuitboard (not shown) in the housing 202 e. In other embodiments, thesensor, microcontroller and memory are contained in separate packagesand connected to one another.

The control unit 204 can be a microcontroller or embedded processorprogrammed with instructions for automatically operating the windowtreatment 104 to permit light according to a predetermined method, basedon the total light intensity and/or the rate of change of the totallight intensity. The control unit 204 includes a tangible,non-transitory machine readable storage medium (e.g., flash memory, notshown) encoded with data and computer program code for controllingoperation of the window treatment.

FIG. 9 is a flow chart of a method of controlling a motorized windowtreatment 104 positioned adjacent to a window 208 on a wall of abuilding.

At step 902, the method samples a total light intensity outside of thebuilding. This measurement is collected by the photosensor 202. If thephotosensor 202 is located outside of the building, it samples the lightdirectly. If the photosensor 202 is mounted on the housing of the windowtreatment 104 inside the building, then the control unit 204 can apply acorrection to the sensor output signal to account for the absorptivityand reflectivity of the window, through which the light penetrates toreach the photosensor 202.

At step 904, the control unit 204 computes a rate of change of the totallight intensity. The rate of change is determined numerically bydividing a difference between two light intensity values by a relevanttime interval. In some embodiments, the difference is computed bydirectly subtracting a first light intensity signal value from a secondlight intensity signal value. Using only two light intensity signalvalues is computationally simple and quick, and provides rapid responseto real changes in lighting conditions. However, if only two sensorsamples are used, the computed difference can incorporate sensor noiseinto the rate of change value, and tends to produce more fluctuations inthe rate of change function. In other embodiments, the total lightintensity samples are summed, averaged, or numerically integrated over ashort sampling period (such as one, two or five minutes, for example).Doing so tends to cancel out random noise and reduce the spikes in thecomputed rate of change values.

At step 906, the control unit 204 determines whether the absolute valueof the rate of change is at least a first threshold value. If theabsolute value of the rate of change is greater than or equal to thefirst threshold value, step 912 is performed. If the absolute value ofthe rate of change is less than the threshold value, step 908 isperformed. For example, in some embodiments, the threshold rate ofchange between sunny and cloudy is 50 to 100 ticks/minute. In otherembodiments, other threshold values are used.

At step 908, a second determination is made, whether the total lightintensity is at least a second threshold value. If the total lightintensity is greater than or equal to the second threshold value, step912 is performed. The second threshold value is set empirically at avalue that is generally exceeded on most sunny days while the solarelevation angle is greater than a threshold angle (for example, but notlimited to, 15 degrees). This corresponds to most daylight time, betweenand excluding sunrise and sunset on sunny days. If the total lightintensity is less than the second threshold value, step 910 isperformed. In some embodiments, the second threshold may be set at about600 foot candles, about 1000 foot-candles. or about 1200 foot candles.In some embodiments, a control on the window treatment allows theoccupant to select the second threshold value.

At step 910, when the computed absolute value of the rate of change isless than the first threshold value and the total light intensity isless than a second threshold value the control unit 204 automaticallycontrols movement of the window treatment 104 in a cloudy operationmode.

At step 912, when the computed absolute value of the rate of change isat least the first threshold value or the total light intensity is atleast a second threshold value, the control unit 204 automaticallycontrols movement of the window treatment in a sunny operation mode.Thus, the control unit 204 automatically controls movement of the windowtreatment in the sunny operation mode if (1) the computed absolute valueof the rate of change is at least the first threshold value or (2) thecomputed absolute value of the rate of change is less than the firstthreshold value and the total light intensity is at least the secondthreshold value.

As noted above, near sunrise and sunset, the total light intensity isrelatively low, even on sunny days. If cloudy day detection is basedsolely on the comparison to a fixed total light intensity value, a sunnycondition can be mistakenly identified as cloudy. At these times, thesun may be very low in the sky and may shine directly into the windowsof the building, thus creating solar penetration conditions.

The inventors have determined that at sunrise and sunset, even thoughthe total light intensity value is relatively low regardless of sunny orcloudy conditions, the absolute value of the rate of change of the totallight intensity tends to be significantly larger on sunny and partiallysunny days than on cloudy days. Thus, the method shown in FIG. 9provides improved discrimination between sunny and partly sunny days onthe one hand and cloudy days on the other hand.

FIG. 10A is an enlarged detail of step 912 of FIG. 9. In thisembodiment, the window treatment has two possible sunny operation modepositions. At step 1002, a determination is made whether the totalintensity of the light is greater than a third threshold value. If so,step 1004 is performed. Otherwise, step 1006 is performed.

At step 1004, the window treatment is moved to a first position (e.g.,fully closed, or from 75% to 90% closed), if the total light intensityis at least a third threshold value.

At step 1006, the window treatment is moved to a second position (e.g.,fully open, or from 15% to 25% open), if the total light intensity isless than the third threshold value.

FIG. 10B is a detail of another implementation of step 912 of FIG. 9. Instep 912B, the window treatment position is varied as a function of thetotal light intensity.

FIG. 10C is a detail of another implementation of step 912 of FIG. 9. Insome embodiments, the window treatment position is varied as a linearfunction of the total light intensity. Thus, the window treatmentposition can be determined by an equation such as:

Y=Y ₀ +C*(Total Light Intensity),

where Y is the window treatment position (e.g., hem bar position for aroller shade, angle for blinds, or the like), Y₀ and C are bothconstants.

Although FIGS. 10A-10C provide three non-limiting examples of the sunnyoperation mode which do not require geographic data, solar time, orother externally supplied dynamic data, a variety of sunny operationmode techniques can be used. For example, in systems with communicationscapability or access to geographic information and solar time, thecontrol unit can control the window treatment in the sunny operationmode to control the solar penetration distance, estimated interiornatural light level, estimated interior heat contribution from solarradiation, or the like.

FIG. 11 is a flow chart showing more details of an implementation of theembodiment of FIG. 9.

At step 1102, the photosensor samples a total light intensity outside ofthe building. If the photosensor 202 is mounted on the housing of thewindow treatment 104 inside the building, then the control unit 204 canapply a correction to the sensor output signal to account for theabsorptivity and reflectivity of the window, through which the lightpenetrates to reach the photosensor 202.

At step 1104, the light intensity values are summed, numericallyintegrated or averaged over plural intervals to provide plural intensityvalues.

In some embodiments, step 1104 computes the average intensity summing oraveraging the sampled total light intensity over each of a plurality ofintervals to provide a respective intensity value for each respectiveinterval. For example, in one embodiment, the total light intensitysignal from the photosensor 202 is sampled every 30 seconds. Each timefive new values are sampled (i.e., every 2.5 minutes), an average totallight intensity value and an average time for that 2.5 minute intervalis computed. Thus, after five minutes, two average total light intensityvalues have been computed. The first average value is based on fivesamples with an average time of 1.25 minutes and the second averagevalue is based on five samples with an average time of 3.75 minutes.

At step 1106, the control unit 204 computes a rate of change of thetotal light intensity. The rate of change is determined numerically bydividing a difference between two average light intensity values by therelevant time interval. In some embodiments, computing the rate ofchange includes calculating the rate of change as the difference betweenfirst and second sampled total light intensities divided by a length oftime between sampling the first total light intensity and sampling thesecond total light intensity.

In the example above, the difference between the two average lightintensity values is divided by (3.75−1.25)=2.5 minutes.

In other embodiments, step 1104 sums (or integrates) the light intensityvalues without calculating an average; and step 1106 compensates byusing a higher threshold for the sum of the intensity values. Forexample, if five intensity values are summed in step 1004 (withoutdividing the sum by five), then the threshold rate of change value canbe multiplied by five, so that the same sunny/cloudy decision will bereached.

At step 1108, the control unit 204 determines whether the absolute valueof the rate of change is at least a first threshold value. If theabsolute value of the rate of change is greater than or equal to thefirst threshold value, step 1014 is performed. If the absolute value ofthe rate of change is less than the threshold value, step 1010 isperformed.

At step 1110, a second determination is made, whether the total lightintensity is at least a second threshold value. If the total lightintensity is greater than or equal to the second threshold value, step1114 is performed. If the total light intensity is less than the secondthreshold value, step 1112 is performed.

At step 1112, when the computed absolute value of the rate of change isless than the first threshold value and the total light intensity isless than a second threshold value the control unit 204 automaticallycontrols movement of the window treatment 104 in a cloudy operationmode. In this example, the control unit 204 automatically controlsmovement of the window treatment 104 to open the window treatment(either fully or to a greatest extent used by the method).

At step 1114, the control unit 204 automatically controls movement ofthe window treatment in the sunny operation mode if (1) the computedabsolute value of the rate of change is at least the first thresholdvalue or (2) the computed absolute value of the rate of change is lessthan the first threshold value and the total light intensity is at leastthe second threshold value. In this example, the window treatment 104 isautomatically moved to a closed or (substantially closed) positionselected to ensure the comfort of the occupant of the room in which thewindow treatment system 200 is located.

By summing, integrating or averaging samples of the total lightintensity sensor signal over a relatively short period of time (e.g., 2to 5 minutes), the effects of sensor noise and small deviations insensor output are reduced. This in turn reduces swings in the computedrate of change of the total light intensity.

FIG. 12A is a flow chart showing operation of the system in the cloudyoperation mode.

At step 1202, a determination is made whether the absolute value of therate of change of the total light intensity is less than a firstthreshold. If the absolute value of the rate of change is less than thethreshold, step 1204 is performed. If the absolute value of the rate ofchange is greater than or equal to the threshold, step 1206 isperformed.

At step 1204 the window treatment is moved to a “visor” position whilethe computed absolute value of the rate of change is less than the firstthreshold value. The visor position is a mostly open position (e.g., 75%to 90% open) which maximizes natural light on cloudy days to minimizelighting loads. The dashed arrow indicates that the evaluation of step1202 is repeated as long as the system operates in the cloudy operationmode.

At step 1206, if the absolute value of the rate of change is greaterthan or equal to the first threshold, the system changes state toautomatically control movement of the window treatment in the sunnyoperation mode.

FIG. 12B shows another feature which is used in some embodiments duringcloudy operation mode. In some embodiments, the system is biased toprotect occupant comfort by responding rapidly to close the windowtreatment if conditions change from cloudy to sunny, while avoidingdistractions due to frequent opening and closing of the windowtreatment. Thus, the steps of FIG. 12B are performed while in the cloudyday mode (i.e., while the absolute value of the rate of change of totallight intensity is less than a first threshold.

At step 1212, a third threshold value is input or selected, such thatthe third threshold is greater than zero, and lower than the firstthreshold value. The third threshold value divides the cloudy operationmode into two zones. When the absolute value of the rate of change islow (less than the third threshold), the system preserves battery lifeby computing the rate of change less often. When the absolute value ofthe rate of change is high (between the third threshold and the firstthreshold, the rate of change is computed more often. As a result, whenthe absolute value of the rate of change crosses above the firstthreshold, there will be a relatively short delay before the rate ofchange is next computed and the system is transitioned to the sunnyoperation mode.

At step 1214, the system computes the rate of change and determineswhether the absolute value of the rate of change is between zero and thethird threshold (low rate of change). If so, the rate of change is low,and step 1218 is performed. If the rate of change is greater than thethird threshold, step 1216 is performed.

At step 1216, the frequency of computing the rate of change becomes (oris maintained) larger.

At step 1218, the frequency of computing the rate of change becomes (oris maintained) less frequent.

In some embodiments, step 1216 uses a first constant frequency and step1218 uses s a second constant frequency, where the first constantfrequency is higher than the second constant frequency. In otherembodiments, the frequency at which the rate of change is computed isvaried as a function of the rate of change. For example, in someembodiments, the frequency of computing the rate of change is a linearfunction of the rate of change.

FIG. 13A is a flow chart of an alternative program flow for controllinga motorized window treatment positioned adjacent to a window on a wallof a building, in which the total light intensity is evaluated first,and then the rate of change of the total light intensity is evaluated.

At step 1302, a total light intensity is sampled outside of thebuilding.

At step 1304, a determination is made whether the total light intensityis at least a first threshold value. If so, step 1312 is performed. Ifnot, then step 1306 is performed.

At step 1306, a rate of change of the total light intensity is computed.

Steps 1308-1310 automatically control movement of the window treatmentbased at least partially on a rate of change of the total lightintensity if the total light intensity is less than the first thresholdvalue.

At step 1308, a determination is made whether the absolute value of therate of change is at least a second threshold value. If the absolutevalue of the rate of change of the total light intensity is at least asecond threshold value. step 1312 is performed, for moving the windowtreatment to a first position. If the absolute value of the rate ofchange of the total light intensity is less than the second thresholdvalue, step 1310 is performed.

At step 1310, the control unit 204 automatically controls movement ofthe window treatment in the cloudy operation mode while the total lightintensity is less than the first threshold value.

At step 1312,

the control unit 204 automatically controls movement of the windowtreatment based on the total light intensity if the total lightintensity is at least a first threshold value.

FIG. 13B shows an embodiment of step 1310 of FIG. 13A. In step 1310A,the control unit 204 causes the window treatment to move to a secondposition if the absolute value of the rate of change of the total lightintensity is less than the second threshold value. For example, thesecond position can be an open or “visor” position used in cloudyoperation mode.

FIG. 13C shows another embodiment of step 1310 of FIG. 13A. In step1310B, the control unit 204 causes the window treatment to move thewindow treatment to a position that varies as a function of the totallight intensity if the absolute value of the rate of change of the totallight intensity is less than a second threshold value. At sub-step 1311,the control unit calculates a second position as a function of the totallight intensity. At sub-step 1313, the control unit 204 causes thewindow treatment to move to the second position

FIG. 14 is a state diagram showing the two operating modes and theallowable transitions in some embodiments.

When the system is operating in the cloudy operation mode 1402, thesystem will cause the window treatment to move to a fully open or“visor” position (75% to 90% open) to maximize natural light and views.In some embodiments, the setting (e.g., height) of the window treatmentin the cloudy operation mode can be set manually by a user. For example,the user actuates a “program” button or control and moves the windowtreatment to the desired cloudy day position. In other embodiments, theuser can select the cloudy day position from a predetermined set ofoptions using a programming button or control.

Because the window treatment is substantially opened in the cloudy mode,a sudden change in lighting conditions (e.g., the sun emerging frombehind a large cloud) can result in glare or discomfort to an occupant.Thus, in some embodiments, the system is biased to respond nearimmediately to such a change. In some embodiments, as soon as acomputation of the rate of change of total light intensity indicatesthat the absolute value of the rate of changes has increased beyond therelevant rate-of-change threshold, the control unit 204 transitions tothe sunny operation mode (state 1404). Similarly, as the total lightintensity has increased beyond the total-light-intensity threshold, thesystem transitions to the sunny operation mode (state 1404). On theother hand, if the rate of change of total light intensity has smalloscillations above and below the rate of change threshold, the controlunit 204 still assumes that this indicates a sunny day. This biastowards treating uncertain situations as being sunny ensures that theoccupant is protected from glare or excessively bright light.

As described above with respect to FIG. 12B, in some embodiments, thefrequency of rate of change computations is increased when the absolutevalue of the rate of change is relatively high (closer to the thresholdfor changing to the sunny operation mode). This further reduces thedelay in performing the next computation of the rate of change after theweather changes, so that the control unit 204 causes transition to thesunny operation mode to occur almost immediately.

In some embodiments, the step of controlling the window treatment in thecloudy day mode includes transitioning to control the window treatmentin the sunny day mode immediately upon determining that the absolutevalue of the rate of change of the total light intensity has increasedto at least the first threshold value. Meanwhile, the step ofcontrolling the window treatment in a sunny day mode includes causingthe window treatment to remain in a sunny day position for at least apredetermined minimum time period before transitioning to a cloudy dayposition.

Referring again to FIG. 14, once the system is operating in the sunnyoperation mode at state 1404, the control unit 204 implements a minimumdelay at step 1406 before the system is returned. This minimizesdistractions due to too-frequent movement of the shades during partlysunny weather, and prolongs battery life. Thus, the transition back tocloudy mode does not occur until the minimum time between shademovements has passed, and the absolute value of the rate of change isless than the relevant threshold.

FIG. 15 is a diagram of another optional feature which can be includedin the control unit 204 to prevent excess distracting movement andbattery consumption. The control unit 204 provides hysteresis using twothresholds, TC and TS (instead of a single threshold). When the systemis in the cloudy operation mode, the control unit 204 does nottransition to the sunny operation mode until the absolute value of therate of change 1502 of the total light intensity is greater than orequal to a sunny threshold TS (at time t1). When the system is in thesunny operation mode, the control unit 204 does not transition to thecloudy operation mode until the absolute value of the rate of change1502 of the total light intensity is less than or equal to a cloudythreshold TC. Thus, in either operation mode, to change state to theother operation mode, the absolute value of the rate of change of thelight intensity first passes through both thresholds. In someembodiments, two thresholds TC, TS are used in combination with theminimum delay of block 1406 (FIG. 14) described above. In otherembodiments, two thresholds TC, TS are used without a minimum delay.

Also shown in FIGS. 14 and 15, for purpose of cloudy day assessment, theabsolute value of the rate of change is used. In the case of a perfectlysunny day with no shadows or obstructions, the rate of change willgenerally be sinusoidal, and will at times be negative. By using theabsolute value of the rate of change, sharp transitions are interpretedas an indication of sunny conditions. A sharp transition can occur on amostly sunny day for example, when the sun goes behind a cloud (largenegative rate of change) or emerges from a cloud (large positive rate ofchange), Both cases involve mostly sunny days, and are treated the sameas a clear sunny day, insofar as control based on the rate of change oftotal light intensity is concerned. Thus for example, between time t2and t3, the rate of change 1502 becomes increasingly negative. At timet3, when the absolute value of the rate of change 1504 (shown inphantom) increases beyond the sunny operation threshold TS, control unit204 again transitions to sunny operation mode. At time t4, when theabsolute value of the rate of change 1504 (shown in phantom) decreasesbelow the cloudy operation threshold TC, control unit 204 againtransitions to cloudy operation mode.

The methods and system described herein may be at least partiallyembodied in the form of computer-implemented processes and apparatus forpracticing those processes. The disclosed methods may also be at leastpartially embodied in the form of tangible, non-transient machinereadable storage media encoded with computer program code. The media mayinclude, for example, RAMs, ROMs, CD-ROMs, DVD-ROMs, BD-ROMs, hard diskdrives, flash memories, or any other non-transient machine-readablestorage medium, wherein, when the computer program code is loaded intoand executed by a computer, the computer becomes an apparatus forpracticing the method. The methods may also be at least partiallyembodied in the form of a computer into which computer program code isloaded and/or executed, such that, the computer becomes a specialpurpose computer for practicing the methods. When implemented on ageneral-purpose processor, the computer program code segments configurethe processor to create specific logic circuits. The methods mayalternatively be at least partially embodied in a digital signalprocessor formed of application specific integrated circuits forperforming the methods.

Although the subject matter has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed broadly, to include other variants and embodiments,which may be made by those skilled in the art.

What is claimed is:
 1. A method of controlling a motorized windowtreatment positioned adjacent to a window on a wall of a building, themethod comprising: sampling a light intensity outside of the building;computing a rate of change of the light intensity; automaticallycontrolling movement of the window treatment in a sunny operation modeif the absolute value of the computed rate of change is at least a firstthreshold value; and automatically controlling movement of the windowtreatment in a cloudy operation mode if the absolute value of thecomputed rate of change is less than the first threshold value and thelight intensity is less than a second threshold value.
 2. The method ofclaim 1, further comprising automatically controlling movement of thewindow treatment in the sunny operation mode if the absolute value ofthe computed rate of change is less than the first threshold value andthe light intensity is at least the second threshold value.
 3. Themethod of claim 1 wherein computing the rate of change furthercomprises: summing or averaging the sampled light intensity over each ofa plurality of intervals to provide a respective intensity value foreach respective interval; and calculating the rate of change as thedifference between ones of the intensity values divided by a length ofone of the intervals.
 4. The method of claim 1 wherein computing therate of change further comprises: calculating the rate of change as thedifference between first and second sampled light intensities divided bya length of time between sampling the first light intensity and samplingthe second light intensity.
 5. The method of claim 1, whereinautomatically controlling movement of the window treatment in the sunnyoperation mode further comprises: moving the window treatment to a firstposition if the light intensity is at least a third threshold value; andmoving the window treatment to a second position if the light intensityis less than the third threshold value.
 6. The method of claim 1,wherein automatically controlling movement of the window treatment inthe sunny operation mode further comprises: moving the window treatmentto a position that is a function of the light intensity.
 7. The methodof claim 1, wherein automatically controlling movement of the windowtreatment in the sunny operation mode further comprises: moving thewindow treatment to a position that is a linear function of the lightintensity.
 8. The method of claim 1, wherein automatically controllingmovement of the window treatment in the cloudy operation mode furthercomprises: moving the window treatment to a visor position while theabsolute value of the computed rate of change is less than the firstthreshold value.
 9. The method of claim 1, wherein a third thresholdvalue is lower than the first threshold value, and the rate of change ofthe light intensity is computed more frequently when the absolute valueof the computed rate of change is between the first threshold value andthe third threshold value than when the absolute value of the computedrate of change is between zero and the third threshold value.
 10. Themethod of claim 1, wherein the method further comprises hysteresis, suchthat automatically controlling movement of the window treatment in thesunny operation mode and in the cloudy operation mode comprisestransitioning between the sunny operation mode and the cloudy operationmode when the rate of change of the light intensity passes through asunny threshold and a cloudy threshold, wherein the sunny threshold ishigher than the cloudy threshold.
 11. A method of controlling amotorized window treatment positioned adjacent to a window on a wall ofa building, the method comprising: (a) sampling a light intensityoutside of the building; (b) computing a rate of change of the lightintensity; (c) automatically controlling movement of the windowtreatment based on the light intensity if the light intensity is atleast a first threshold value; and (d) automatically controllingmovement of the window treatment based at least partially on the rate ofchange of the light intensity if the light intensity is less than thefirst threshold value.
 12. The method of claim 11, wherein (d) furthercomprises moving the window treatment to a first position if an absolutevalue of the rate of change of the light intensity is at least a secondthreshold value.
 13. The method of claim 12, wherein (d) furthercomprises moving the window treatment to a second position if theabsolute value of rate of change of the light intensity is less than thesecond threshold value.
 14. The method of claim 11, wherein (d) furthercomprises moving the window treatment to a position that varies as afunction of the light intensity if the absolute value of the rate ofchange of the light intensity is less than a second threshold value. 15.The method of claim 11, wherein (d) further comprises: controlling thewindow treatment in a sunny day mode if the absolute value of the rateof change of the light intensity is greater than or equal to a secondthreshold value; and controlling the window treatment in a cloudy daymode if the absolute value of the rate of change of the light intensityis less than the second threshold value.
 16. The method of claim 15,wherein controlling the window treatment in the sunny day mode comprisescausing the window treatment to remain in a sunny day position for atleast a predetermined minimum time period before transitioning to acloudy day position.
 17. The method of claim 15, wherein controlling thewindow treatment in the cloudy day mode comprises transitioning tocontrolling the window treatment in the sunny day mode immediately upondetermining that the absolute value of the rate of change of the lightintensity has increased to at least the second threshold value.
 18. Asystem comprising: a motorized window treatment adapted to be positionedadjacent to a window on a wall of a building: a sensor for sampling alight intensity outside of the building; and a processor configured to:compute a rate of change of the light intensity, automatically controlmovement of the window treatment in a sunny operation mode if theabsolute value of the computed rate of change is at least a firstthreshold value, and automatically control movement of the windowtreatment in a cloudy operation mode if the absolute value of thecomputed rate of change is less than the first threshold value and thelight intensity is less than a second threshold value.
 19. The system ofclaim 18, wherein the processor is further configured to automaticallycontrol movement of the window treatment in the sunny operation mode ifthe absolute value of the computed rate of change is less than the firstthreshold value and the light intensity is at least the second thresholdvalue.
 20. The system of claim 18, wherein to automatically controlmovement of the window treatment in the sunny operation mode comprisesto: move the window treatment to a first position if the light intensityis at least a third threshold value; and move the window treatment to asecond position if the light intensity is less than the third thresholdvalue.
 21. A system comprising: a motorized window treatment adapted tobe positioned adjacent to a window on a wall of a building, comprising:a sensor for sampling a light intensity outside of the building; and aprocessor configured to: compute a rate of change of the lightintensity; automatically control movement of the window treatment basedon the light intensity if the light intensity is at least a firstthreshold value; and automatically control movement of the windowtreatment based at least partially on the rate of change of the lightintensity if the light intensity is less than the first threshold value.22. The system of claim 21, wherein the processor is further configuredto move the window treatment to a first position if the absolute valueof the rate of change of the light intensity is at least a secondthreshold value.
 23. The system of claim 22, wherein the processor isfurther configured to move the window treatment to a second position ifthe absolute value of rate of change of the light intensity is less thanthe second threshold value.
 24. The system of claim 21, wherein theprocessor is further configured to: control the window treatment in asunny day mode if the absolute value of the rate of change of the lightintensity is greater than or equal to a second threshold value; andcontrol the window treatment in a cloudy day mode if the absolute valueof the rate of change of the light intensity is less than the secondthreshold value.
 25. The system of claim 24, wherein to control thewindow treatment in a sunny day mode comprises to cause the windowtreatment to remain in a sunny day position for at least a predeterminedminimum time period before transitioning to a cloudy day position.